# [Gmsh] generate a "regular" mesh for a simple cylinder

Shi Jin jinzishuai at yahoo.com
Wed Sep 12 01:31:19 CEST 2007

```Hi there,

I have a quite simple task: generate a unstructured
1st order tetrahedral grid for a cylinder. There is
nothing fancy in the domain however I have a
requirement that the generated mesh should look a bit
"regular", meaning that it should be well structured
as "layers" along the axis direction. I want this
feature since it is then easy for me to divide the
domain into simple chunks for parallel computation.

I found a almost working solution: use extrusion with
layers. First I create a circle on a plane (by
rotating a   quarter of circle arc 3 times) and then
extrude it with layers. The resulting mesh looks
exactly like what I have in mind. However, there is
one issue: in the node list, there is a point for the
center of the circles (at each layer after extrusion).
However, these points are not used in the mesh. In the
example I provide below, a new point very close the
the center (1e-15,1e-15) is created rather using the
(0,0) point. I guess this shouldn't be a big deal for
most solvers but the particular package I am using
does not allow the number of nodes to be different
from the total number of nodes computed from
connectivity table.
I am wondering if you can help solve the problem.

I can think of two ways to overcome the issue:
1. Remove the center point. However, I found that I am
not able to remove this point with the circle arc
defined.
2. Enforce the mesh to use the center points but I
don't know how to either.

In the attachment, I am providing a simple .geo file
that demonstrate the problem and its corresponding
.msh file. Note that in the node list of the
cylinder.msh file, point 3 and 7 are never used while
point 19 and 20 are actually just O(1e-15) close by.

Thanks.
Shi

____________________________________________________________________________________
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```